On Wed, 2023-03-01 at 10:07 -0800, Rick Edgecombe wrote: > > If one wants to scan the shadow stack how to detect the end (e.g. > > fast > > backtrace)? Is it useful to put an invalid value (-1) there? > > (affects map_shadow_stack syscall too). > > Interesting idea. I think it's probably not a breaking ABI change if > we > wanted to add it later. One complication could be how to handle shadow stacks created outside of thread creation. map_shadow_stack would typically add a token at the end so it could be pivoted to. So then the backtracing algorithm would have to know to skip it or something to find a special start of stack marker. Alternatively, the thread shadow stacks could get an already used token pushed at the end, to try to match what an in-use map_shadow_stack shadow stack would look like. Then the backtracing algorithm could just look for the same token in both cases. It might get confused in exotic cases and mistake a token in the middle of the stack for the end of the allocation though. Hmm...
